1. Field of the Invention
The present invention relates to a method and an apparatus for manufacturing a prepreg, in which the prepreg is made of a fibrous reinforcing substrate coated and impregnated with a thermosetting matrix.
2. Description of Background Information
Japanese Laid-Open Patent Application No. HEI 8-281645 discloses a technique for continuously manufacturing a prepreg by allowing a long sheet-shape fibrous reinforcing substrate to be coated and impregnated with a thermosetting matrix resin containing no solvent while the reinforcing substrate travels.
In detail, this technique shows a prepreg manufacturing method which includes a first coating process for applying a thermosetting matrix resin containing no solvent in a molten state onto one surface of a sheet-shape reinforcing substrate by using a die coater, a process for heating the reinforcing substrate coated with the thermosetting matrix resin by a heating unit of a non-contact type so that the reinforcing material is impregnated with a thermosetting matrix resin, a second coating process for applying a thermosetting matrix resin to the reinforcing substrate impregnated with the thermosetting matrix resin on its surface opposite to the resin-coated surface by the first coating process by using a die coater, and a process for heating the reinforcing substrate coated and impregnated with the thermosetting matrix resin by a heating unit of a non-contact type so as to semi-cure the thermosetting matrix resin to form a sheet-shape prepreg.
However there are some problems in this technique. That is, since a die coater is used to apply the thermosetting matrix resin onto the reinforcing substrate, the thermosetting matrix resin tends to easily adhere to the inside of the die coater. Accordingly, the coating precision deteriorates and long time is required to clean and maintain the die coater. Moreover, although a die coater itself is very expensive device, it is necessary that two die coaters are respectively placed on one surface and on another surface of the reinforcing substrate so as to apply the thermosetting matrix resin on the respective surfaces. As a result, equipment costs are high. Furthermore, since the thermosetting matrix resin is applied to the both surfaces of the reinforcing substrate, air inside the reinforcing material tends to be entrapped by the matrix resin. Accordingly, voids are likely to occur in the prepreg.